1. Field of the Invention
The present invention relates to radiation imaging apparatuses and radiation imaging systems. More specifically, for example, the present invention relates to a radiation imaging apparatus and system that are suitable for still-picture imaging, such as ordinary imaging, or moving-picture imaging, such as fluoroscopy, in medical diagnosis. In the present invention, in addition to α rays, β rays, and γ rays formed of particles (including photons) emitted by radioactive decay, radiation rays include beams having the same or greater order of energy, for example, X rays, corpuscular rays, and cosmic rays.
2. Description of the Related Art
Recently, as radiation imaging apparatuses are being used for X-ray medical image diagnosis or non-destructive testing, radiation imaging apparatuses including flat panel detectors (hereinafter abbreviated as “FPDs”) composed of semiconductor materials are coming into practical use. In a radiation imaging apparatus including an FPD, radiation rays, such as X rays, that have transmitted through a subject, such as a patient, are converted into analog electric signals by the FPD, and analog-to-digital conversion is executed to convert the analog electric signals into digital image signals, whereby a digital image is obtained. FPDs can be broadly classified into direct-conversion FPDs and indirect-conversion FPDs. A direct-conversion radiation imaging apparatus includes an FPD having a two-dimensional array of pixels including semiconductor-based converters that directly convert radiation rays emitted from a-Se or the like into charges. An indirect-conversion radiation imaging apparatus includes an FPD having a two-dimensional array of pixels each including a converter having a wavelength converter and a photoelectric converter element. The waveform converter is implemented, for example, by a phosphor member capable of converting radiation rays into visible light. The photoelectric converter element is composed of a semiconductor material capable of converting light into charges, such as a-Si. The indirect-conversion radiation imaging apparatus is disclosed, for example, in Japanese Patent Laid-Open No. 08-116044. These radiation imaging apparatuses including FPDs can convert radiation images into digital information, so that image information can be transmitted instantly to a remote location. For example, in the field of medical image diagnosis, the radiation imaging apparatuses including FPDs are used as digital imaging apparatuses for still-picture imaging such as ordinary imaging or moving-picture imaging such as fluoroscopy.
With the radiation imaging apparatuses including FPDs composed of semiconductor materials, reduction of power consumption is an issue to be addressed. According to techniques disclosed in Japanese Patent Laid-Open No. 2005-270656, the FPD and a driving circuit for driving the FPD or a reading circuit for reading signals from the FPD are powered on until a cycle of an irradiating sequence and imaging is completed, and these components are caused to be idle or powered off in other periods, so that power consumption is reduced.